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Biomedical subjects

A M Summers

Publications and source records attributed to A M Summers.

15 recordsLinked to original sources
PubMed2005

The effect of fetal gender on the false-positive rate of Down syndrome by maternal serum screening.

OBJECTIVES: (1) To further explore if there is a difference in maternal serum levels of alpha-fetoprotein (AFP), human chorionic gonadotrophin (hCG) and estriol (uE3) between fetal genders. (2) To determine if these differences influence false-positive rates of Down syndrome screening in pregnancies with male or female fetuses. METHODS: This is a descriptive study of women screened at the Ontario Maternal Serum Screening program between 1993 and 1995. The women were grouped by fetal gender and ethnicity. Serum levels of the three markers and screening false-positive rates for Down syndrome were compared between fetal genders in women of different ethnicity respectively. RESULTS: Complete data were available for 110 306 pregnancies. In all three ethnic groups, MSAFP levels were significantly decreased and MShCG levels were significantly increased in women with female fetuses. The level of MSuE3 was similar between genders. The difference in false-positive rates of Down syndrome between genders was not statistically significant. CONCLUSIONS: This is the largest study comparing false-positive rates between fetal genders. In contrast to previous studies, the differences in the serum marker levels between fetal genders do not influence the false-positive rates for Down syndrome.

Adult↗
PubMed2005

The influence of risk estimates obtained from maternal serum screening on amniocentesis rates.

OBJECTIVE: To investigate the influence of Down syndrome risk estimates obtained from maternal serum screening (MSS) on women's choices regarding amniocentesis. METHODS: Women who screened positive for Down syndrome by an Ontario MSS program between 1993 and 1998 were grouped on the basis of their risk estimate and ethnicity. Amniocentesis uptake rates between the groups were compared in order to determine how the MSS risk estimate influenced uptake. RESULTS: Analysis of 16 792 women showed that amniocentesis uptake rates increased as the estimated risk increased. Uptake in women < or = 35 was higher than that for older women (70% vs 60%, p = 0.001). Uptake in Caucasian and Asian women was higher than the uptake in Black women (67% vs 49%, p = 0.001). Women aged 35 years or older were more likely to proceed with amniocentesis if the MSS risk estimate was higher than their age-specific risk. CONCLUSION: The increase in amniocentesis rate paralleled the increase in MSS risk estimate for Down syndrome. Risk-specific amniocentesis rates are higher in women aged less than 35 years. Women aged 35 years or older whose risk estimate by MSS is lower than their age-specific risk are less likely to opt for amniocentesis.

Adolescent↗
PubMed2003

Maternal serum screening in Ontario using the triple marker test.

OBJECTIVES: To summarise the experience and evaluate the performance of the Ontario maternal serum screening (MSS) programme. SETTING: The Ontario MSS programme between October 1993 and September 2000. METHODS: This study used information collected in the Ontario MSS database, which contains data on each screened pregnancy. In the Ontario MSS programme, women are screened between 15 and 20 weeks of gestation. The risk cut-off for Down's syndrome was >or= 1 in 385 at term and women with a serum alpha-fetoprotein >or= 2.2 multiples of the unaffected population median were defined as screen-positive for open neural tube defects. RESULTS: Between 1 October 1993 and 30 September 2000, 428410 women residing in Ontario were screened for open neural tube defects, and 423895 women were screened for Down's syndrome and trisomy 18. Approximately 48% of all pregnant women in the province had MSS. The uptake rate of amniocentesis following a positive Down's syndrome screening was 67%. Of 717 cases of Down's syndrome ascertained in the screened population, 531 were detected by MSS, giving a term detection rate (DR) of 70.6%, with a false-positive rate (FPR) of 7.2%. For neural tube defects, the DR was 72.7%, with a FPR of 2.0%. The screen also detected 50% of cases of trisomy 18 at term, with a FPR of 0.2%. Coincidentally, 113 cases of chromosome aneuploidies other than Down's syndrome and trisomy 18 were detected. DISCUSSION: In the Ontario MSS programme, MSS performed as expected in the detection of Down's syndrome, open neural tube defects and trisomy 18. MSS is an effective and practical method for large-scale second trimester screening for Down's syndrome, open neural tube defects and trisomy 18, and the MSS database is an extremely useful tool in monitoring the performance of this screen.

Amniocentesis↗
PubMed2000

Association of IL-10 genotype with sudden infant death syndrome.

Sudden infant death syndrome (SIDS) is a major cause of infant death of unknown etiology. We propose that SIDS results from a genetically determined imbalance in the production of inflammatory and anti-inflammatory cytokines in response to the infant's microbial flora. We were especially interested to know the relationship between SIDS and genetically determined higher or lower production of IL-10, an anti-inflammatory cytokine. Biallelic polymorphisms in the promoter region of the IL-10 gene associated with higher or lower production of IL-10 were determined in a SIDS and in a control group using a sequence-specific oligonucleotide approach. One particular allele of the IL-10 gene, the IL-10-592*A allele, was significantly associated with SIDS. Indeed, 70% of the SIDS babies carried the IL-10-592*A allele (p = 0.007 compared with control). In addition, there was a significant reduction in the frequency of homozygosity for the allele IL-10-592*C (p = 0.001 compared with control). Carrying the A allele (either A/A or A/C) had an odds ratio of 3.3 (95% confidence interval 1.4-8.0). In the same patients there was no association with other IL-10 gene polymorphisms nor with other cytokine (TNF-alpha, TGF-beta 1) genotypes, emphasizing the particular relationship between SIDS and the IL-10-592*A allele.

Alleles↗
PubMed2000

Molecular mechanism for duplication 17p11.2- the homologous recombination reciprocal of the Smith-Magenis microdeletion.

Recombination between repeated sequences at various loci of the human genome are known to give rise to DNA rearrangements associated with many genetic disorders. Perhaps the most extensively characterized genomic region prone to rearrangement is 17p12, which is associated with the peripheral neuropathies, hereditary neuropathy with liability to pressure palsies (HNPP) and Charcot-Marie-Tooth disease type 1A (CMT1A;ref. 2). Homologous recombination between 24-kb flanking repeats, termed CMT1A-REPs, results in a 1.5-Mb deletion that is associated with HNPP, and the reciprocal duplication product is associated with CMT1A (ref. 2). Smith-Magenis syndrome (SMS) is a multiple congenital anomalies, mental retardation syndrome associated with a chromosome 17 microdeletion, del(17)(p11.2p11.2) (ref. 3,4). Most patients (>90%) carry deletions of the same genetic markers and define a common deletion. We report seven unrelated patients with de novo duplications of the same region deleted in SMS. A unique junction fragment, of the same apparent size, was identified in each patient by pulsed field gel electrophoresis (PFGE). Further molecular analyses suggest that the de novo17p11.2 duplication is preferentially paternal in origin, arises from unequal crossing over due to homologous recombination between flanking repeat gene clusters and probably represents the reciprocal recombination product of the SMS deletion. The clinical phenotype resulting from duplication [dup(17)(p11.2p11.2)] is milder than that associated with deficiency of this genomic region. This mechanism of reciprocal deletion and duplication via homologous recombination may not only pertain to the 17p11.2 region, but may also be common to other regions of the genome where interstitial microdeletion syndromes have been defined.

Abnormalities, Multiple↗
PubMed2000

Apparently unstable normal FMR1 alleles in nine developmentally delayed patients: implications for molecular diagnosis of the fragile X syndrome.

The Fragile X syndrome is a common form of X-linked mental retardation, affecting approximately 1 in 4,000 males. Since the discovery of the FMR1 gene responsible for the syndrome, molecular, rather than cytogenetic, diagnosis of Fragile X syndrome has become the gold standard. Numerous molecular diagnostic centers worldwide use PCR and Southern blotting to characterize the size of the CGG repeats within the gene, expansion of which has been shown to be associated with the vast majority of cases of Fragile X syndrome. Instability of this repeat through successive generations has been demonstrated in many patients and has been associated with numerous factors, including repeat length and molecular structure of the repeat. Nine males with normal-size alleles that exhibit repeat length instability by the presence of a second normal length distinct band by repeated PCR analysis from peripheral lymphocytes are reported. Many hypotheses addressing the reason for this apparent instability were tested without elucidating the underlying molecular causes, including cytogenetic analysis, sequence analysis of the repeat locus, and analysis of flanking dinucleotide repeat loci. All patients exhibited a normal complement of sex chromosomes by cytogenetic and molecular analysis. These results from the widely used PCR analysis illustrate an interesting molecular phenomenon and raise many questions relating to the factors and mechanisms involved in trinucleotide instability as well as having implications for the diagnostic testing of the Fragile X syndrome.

Alleles↗
PubMed1999

Club foot, an adverse outcome of early amniocentesis: disruption or deformation? CEMAT. Canadian Early and Mid-Trimester Amniocentesis Trial.

An association between the occurrence of club foot and early amniocentesis has been reported. The largest of these randomised studies was the Canadian Early and Mid-Trimester Amniocentesis Trial. Data describing the neonatal outcome, focusing on this association, are presented. Possible mechanisms for the association and the implications for the development of club foot are discussed.

Adult↗
PubMed1993

Interstitial deletion of chromosome 10q23: a new case and review.

A new case of a deletion of 10q23 is described. Only two other deletions involving this region have been previously noted. A review of clinical features of these three children did not show a distinct pattern of dysmorphic features. Other interstitial deletions of 10q are listed.

Abnormalities, Multiple↗
PubMed1992

X-linked recessive Charcot-Marie-Tooth neuropathy: clinical and genetic study.

We describe three families with X-linked recessive Charcot-Marie-Tooth (CMT) neuropathies. The disease phenotype in family 1 was characterized by infantile onset, weakness of lower legs, areflexia, pes cavus, and mental retardation (2 of 5 patients). The disease phenotype in families 2 and 3 was characterized by late onset, distal weakness, and normal intelligence. Hereditary spastic paraparesis was also present in the CMT patients of family 2. Thirty X-linked DNA markers were used for linkage studies. A maximum lod score of +3.48 was obtained by multipoint linkage analysis for the DXS16 locus mapped at Xp22.2 in family 1. In families 2 and 3, there was suggestion of linkage of Xq26 markers; the peak multipoint lod score for these 2 CMT families was 1.81, at DXS144. These results were suggestive of heterogeneity. The joint analysis including both regions (Xp22.2 and Xq26) provided evidence against homogeneity (chi 2 = 9.12, P less than 0.005).

Charcot-Marie-Tooth Disease↗
PubMed1991

Heterogeneity in X-linked recessive Charcot-Marie-Tooth neuropathy.

Three families presenting with X-linked recessive Charcot-Marie-Tooth neuropathies (CMT) were studied both clinically and genetically. The disease phenotype in family 1 was typical of CMT type 1, except for an infantile onset; two of five affected individuals were mentally retarded, and obligate-carrier females were unaffected. Families 2 and 3 showed distal atrophy with weakness, juvenile onset, and normal intelligence. Motor-nerve conduction velocities were significantly slowed, and electromyography data were consistent with denervation in affected CMT males in all three families. Thirty X-linked RFLPs were tested for linkage studies against the CMT disease loci. Family 1 showed tight linkage (recombination fraction [theta] = 0) to Xp22.2 markers DXS16, DXS143, and DXS43, with peak lod scores of 1.75, 1.78, and 2.04, respectively. A maximum lod score of 3.48 at DXS16 (theta = 0) was obtained by multipoint linkage analysis of the map DXS143-DXS16-DXS43. In families 2 and 3 there was suggestion of tight linkage (theta = 0) to Xq26 markers DXS86, DXS144, and DXS105, with peak lod scores of 2.29, 1.33, and 2.32, respectively. The combined maximum multipoint lod score of 1.81 at DXS144 (theta = 0) for these two families occurred in the map DXS10-DXS144-DXS51-DXS105-DXS15-DXS52++ +. A joint homogeneity analysis including both regions (Xp22.2 and Xq26-28) provided evidence against homogeneity (chi 2 = 9.12, P less than .005). No linkage to Xp11.12-q22 markers was observed, as was reported for X-linked dominant CMT and the Cowchock CMT variant. Also, the chromosomes 1 and 17 CMT loci were excluded by pairwise linkage analysis in all three families.

Charcot-Marie-Tooth Disease↗